Precast segment for wind turbine tower and method for building a wind turbine tower using said precast segment

ABSTRACT

Precast segment for wind turbine tower especially designed to be used in wind turbine towers installed in cold climates, and which comprises joint flanges showing a configuration intended to establish the boundaries for forming the joints between said precast segment and an adjacent precast segment and which comprises conduits provided with an inlet and an outlet, situated in the proximity of the joint flanges of the precast segment intended to house some heating cables that generate heat. The method comprises the use of the described precast segment and the stages of introducing heating cables in the conduits of the precast segment, applying current to said cables and removing the cables when a filler material used in the joint between precast segments has set.

OBJECT OF THE INVENTION

The present invention can be included in the technical field of precastsegments for wind turbine towers and more specifically for wind turbinetowers in cold climates, where ambient temperature is below 5° C. At thesame time, the invention comprises the method for manufacturing a windturbine tower using the described precast segment.

BACKGROUND OF THE INVENTION

The objective of wind energy is to generate electricity from the windusing wind turbines at maximum possible efficiency and minimum cost.Said wind turbines basically consist of a tower, a nacelle whichcontains the electrical generator,

and a rotor comprising at least two blades.

The tower supports all the elements incorporated in the nacelle andtransmits to the foundations all the reaction forces generated as aconsequence of the wind turbine's different aerodynamic actions andoperating conditions.

Generally, given the dimensions of the wind turbine and consequently, ofthe tower, the latter is manufactured using modular sections ofreinforced concrete called precast segments. To join these precastsegments it is necessary to use a filler material, which may consist ofmortar (also called grout) or a resin, deposited in them.

From now onwards the invention will be explained making reference to theuse of mortar as filler, although it could be, as mentioned, resin oranother material.

During the assembly of concrete towers at low temperatures it isnecessary to guarantee minimum temperature conditions (at least 5° C.)for both the precast segments and the mortar before pouring the mortar,including the temperature of the mortar poured into the vertical andhorizontal joints, to guarantee adequate curing so that the mortar candevelop all its mechanical properties (resistance).

When these assemblies are made at low temperatures, where thetemperature can drop to −20° C., in order to ensure a correct structuralbehaviour of the towers, it is necessary to have a heating system thatallows the temperature to be maintained above 5° C. in both the precastsegments and the mortar poured into the joints.

Pouring mortar at ambient temperatures below 0° C. is always a fairlyrestrictive conditioning factor. This is due to the fact that concreterequires a certain temperature for the cement to hydrate and acquireresistance. Also, because it contains water, there is a risk that whenit starts to set, free-running water freezes increasing its volume, withthe ensuing danger of cracking.

In the case of assembling concrete towers at low temperature, the volumeof mortar is insufficient to guarantee that the water will not freeze,as it is totally surrounded by a large mass of prefabricated concretewhich is at ambient temperature.

In low temperature conditions (below 5° C.) in addition to ensuring themechanical properties of the mortar, it is necessary to guarantee theperfect filling of the joints between the precast segments that make upthe tower.

To this effect, it must be feasible to pump said mortar to a height of20 m with no segregation occurring upon pouring it from a height of 20metres in free fall, in the case of vertical joints. Horizontal jointsare even more restrictive as in this case, the pouring of the mortarmust be guaranteed at heights above 100 m. It is required for allmortars, according to their technical datasheet, that the temperature ofthe support (in the case of towers for wind turbines these are theprecast segments) is at a temperature of at least +5° C. to guaranteecorrect curing. Below 5° C. manufacturers do not guarantee the necessaryminimum resistances.

Traditionally, in the closest prior art, foundations are made at −20° C.using concrete with high cement content so that it has a high heat ofhydration and heats up quick enough to avoid freezing. Generally,footings are covered with thermal blankets so as not to lose too muchheat and in this way maintain the temperature at the required values.

The problem with using thermal blankets is that they need to adhere wellto the surfaces that require heating. If said blankets are notwell-adhered, the heating of the surfaces is slow and non-homogeneous.

Another possibility for heating consists of using fans with anelectrical resistance (cylindrical conduits with directional air outletnozzles) directed towards the joints. Some of the problems that arisewith this solution are that a high number of fans is necessary, makingit necessary to have a high number of generators to supply energy to thefans, and that a certain assurance of continuous system operation isnecessary as a stoppage would entail the rapid loss of the thermalconditions previously generated.

Other alternatives considered in the pre-heating are the use of infraredlamps. The market solutions do not achieve effective results whereheating is concerned.

The current technique for pouring mortar presents four clear drawbacks,among which one would highlight the problems with cracking due tofreezing of the water present, quality problems in the formation of thejoints, filling problems (especially in horizontal joints at heightsthat are distant from the ground), and problems with the resistancecapacity of the mortar when the temperature reached is below 5° C.,problems with assembly in relation to both times and means employed(difficulty with pumping, heating of the nearby medium where the mortaris deposited . . . etc.), and the need to use special mortars with ahigh content in cement with the ensuing increase in the expensiveness ofthe tower.

The heating system known in the state of the art designed to the thermalconditioning of the materials to resolve the problems described abovepresent a high consumption due to low thermal efficiency.

DESCRIPTION OF THE INVENTION

The present invention describes a precast segment for wind turbinetowers and a method for manufacturing wind turbine towers using saidprecast segment. The proposed precast segment and manufacturing methodhelp to resolve the problem of curing the filler material in thevertical and horizontal joints of constructive structures in coldclimates wherein the ambient temperature is below 5° C. Morespecifically, both the design of the precast segment and the methoddescribed allow the use of an optimal heating system of the precastsegments in the zone close to the joints between precast segments.Likewise, they allow adequate setting of the filler material depositedbetween the vertical and horizontal joints of the precast segments usedin the wind turbine tower. One additional advantage of the proposedprecast segment and method is that after being used in a precastsegment, the heating system can be reused for the thermal conditioningof another precast segment.

The precast segment of the present invention is designed to be used inwind turbine towers and comprises at least one joint flange which showsa configuration designed to establish a boundary to form at least onejoint between adjacent precast segments using a filler material that canbe mortar or resin.

To be able to be used in wind turbine towers that are installed in zoneswith cold climates, the proposed precast segment comprises conduitslocated in the vicinity of the joint flanges which are designed to househeating cables. When a current passes through said heating cables, heatis generated.

Said conduits may be coated to enable a more simple introduction andextraction of the heating cables which are introduced into them toincrease the temperature in that zone of the precast segment duringmanufacturing of the wind turbine tower. In one preferred embodiment,the coating comprises at least one layer of lubricant material allowingthe heating cables to slide easily inside the conduits.

Therefore, the conduits of the precast segment are designed to allow thepassage of heating cables which help to heat the joint flanges of theprecast segment that form the joints with the adjacent precast segments.They also help to heat the mortar that is poured into the joints tomaintain the joint between the adjacent precast segments. This makes itpossible to use the described precast segments in wind turbine towersinstalled in cold climate areas. When the mortar of the joint hasacquired a sufficient degree of setting (understood as the level ofsetting at which the mortar has the necessary minimum mechanicalresistance capacity for the joint that encloses it), the heating cablescan be extracted from the inside of the conduit and introduced in theconduits of other precast segments to carry out the same operation.

In one preferred embodiment of the invention, the heating cables arehoused inside the conduits and are part of the precast segment. Saidheating cables may also be coated in a lubricant material to facilitateintroduction thereof into the conduits. It may be the case that both theheating cables and the inside of the conduits comprise a lubricantcoating. Also, the conduits may be pipes made of a material with a highthermal conductivity.

A method for manufacturing wind turbine towers using the precastsegments like the one of the invention which incorporates at least oneheating cable inside the conduits is also described.

To carry out the method, the precast segments are laid out adjacent toeach other, forming a joint between precast segments. Once the precastsegments have been assembled with the heating cables already insidethem, an electrical current is made to flow through said heating cablesand the filler material is poured into the joint while the joint flangesof the precast segments remain hot through the action of the heatingcables. The filler material is preferably mortar or resin. In this way,correct setting of the filler material is ensured even in cold climateswith low ambient temperatures. The placement of the heating cables inthe conduits in proximity to the joint flanges of the precast segments,around the joints, allows the local areas into which the mortar will bepoured to be heated in an optimal manner.

When the mortar has acquired sufficient setting the heating cables areremoved from the conduits. These same heating cables can be used tomanufacture other constructive structures, thereby reducing the costs ofmanufacturing said structures as it is not necessary to buy new heatingcables for each new constructive structure.

Another option considered in the present invention is that the heatingcables remain embedded in the precast segment. In this case, it isnecessary that the precast segments of the constructive structure aremanufactured with reinforcements inside, in other words, withreinforcing steel inside. In this case, internally in the precastsegment, the heating cables are joined to the reinforcements. Theheating cables remain embedded in the precast segment.

When the heating cables are placed directly joined to the reinforcementsof the precast segments a large number of cable fixing points arenecessary. This is due to the fact that the heating cables aredeformable and it must be guaranteed that the distance to the jointflange that forms the joint is substantially the same throughout theentire flange of the joint to guarantee that all the mortar that ispoured into the joint sets under the same conditions.

The present invention guarantees a fast and simple positioning of theheating cables with respect to the joint thanks to the construction ofthe conduits in the precast segments. Said conduits do not compriseright angles to facilitate the insertion and removal of the heatingcables.

The conduits into which the heating cables are inserted have a highthermal conductivity and may be placed taking advantage of thereinforcements in the precast segments, by joining the cables to them ifthe precast segment has reinforcements, or by building the conduits whenthe formwork operation of the precast segments is performed.

In one embodiment of the invention wherein the conduit is a pipe with ahigh mechanical resistance, and more specifically a metal pipe, which isleft embedded in the concrete, said conduit can comprise fins on theoutside to maximise the contact surface with the concrete.

The wind turbine tower formed with the precast segments of the inventionand following the described method have all the vertical and horizontaljoints joined together using mortar. The method used to form them allowsminimum temperature conditions (5° C.) to be guaranteed in both thejoint flanges of the precast segments before pouring the mortar and themortar poured into the joints. This ensures adequate curing and themortar can develop all its mechanical (resistance) properties. This isessential in wind turbine towers which have to withstand very highstresses due to the fact that they are always installed in zones withstrong gusts of wind and that the action of the wind on the wind turbineblades carries strong forces through the tower.

DESCRIPTION OF THE DRAWINGS

To complement the description and with a view to contributing to abetter understanding of the characteristics of the invention inaccordance with a preferred example of a practical embodiment thereof, aset of drawings is attached as an integral part of said descriptionwherein, by way of illustration and not limitation, the following hasbeen represented:

FIG. 1 a.—Shows a close-up plan view of a vertical joint formed betweentwo adjacent precast segments.

FIG. 1 b.—Shows a view of one of the precast segments which appears inFIG. 1 a wherein the conduits can be seen placed in one of its verticaljoint flanges.

FIG. 2 a.—Shows a view of a horizontal joint formed between two adjacentprecast segments.

FIG. 2 b.—Shows a plan view of one of the precast segments that appearsin FIG. 2 a with the conduits placed in one of its horizontal jointflanges.

FIG. 3.—Shows a view of a precast segment with blind conduits whereinthe inlet and the outlet coincide and are placed in one of the verticaljoint flanges of the precast segment.

FIG. 4.—Shows a view of a precast segment with a close-up of a conduitformed by a pipe with fins to increase the thermal conductivity embeddedin the concrete.

FIG. 5 a.—Shows a view of a precast segment with conduits in itsvertical flange and a close-up view in which the pipe that forms theconduit, the lubricant material and the heating cable can beappreciated.

FIG. 5 b.—Shows a view of a precast segment with conduits on itsvertical flange as in FIG. 5 a but in this one the pipe has beenremoved.

PREFERRED EMBODIMENT OF THE INVENTION

The present invention describes a precast segment for wind turbinetowers installed in zones with cold climates and a method formanufacturing wind turbine towers using said precast segment. Theobjective of the invention is to allow local heating of the precastsegments of the wind turbine tower in the zones of interest to allow acorrect setting of the mortar or cement that is poured into the jointsbetween precast segments.

In particular, the invention is especially advantageous in the case ofconcrete towers, normally built using precast segments made of concreteand a metal reinforcement inside consisting of interwoven steel rods,commonly referred to as reinforcements.

The precast segment of the present invention comprises at least onejoint flange (3) which shows a configuration designed to establish alimit to form the at least one joint (4) between said precast segmentand a contiguous precast segment using a filler material. The mostimportant characteristic of the proposed precast segment is that itcomprises conduits (2) provided with an inlet (9) and an outlet (10),situated in the proximity of the joint flanges (3) and which aredesigned to house some heating cables (1).

The heating cables are designed to generate heat when an electricalcurrent is made to pass through them.

Said heating cables (1) can form part or not of the precast segmentitself and are introduced into the conduits (2) through the inlet (9)and removed through the outlet (10). To facilitate these operations, theconduit (2), the heating cables (1) or both may have a coating (7).Additionally, said coating may comprise at least one layer of alubricant material (7).

In one embodiment which can be appreciated in FIG. 5 .b, the conduits(2) are defined by the concrete itself of the precast segments, and havebeen left formed in the manufacture of the precast segments by means ofthe use of inserts.

In one alternative embodiment, the conduits (2) may be pipes (11) of amaterial with a high structural resistance such as steel for example,which are left embedded in the concrete of the precast segment. In thiscase, in addition to acting as a housing and guide for the heatingcables, they would act as a structural reinforcement of the precastsegment itself.

In another embodiment, the conduits (2) are pipes made of a materialwith a low structural resistance in which case they act only as ahousing and a guide.

In addition, the pipes (11) may be made of a material with a highthermal conductivity to boost the effect of the heat that is generatedin the heating cables (1) when an electrical current is applied to them.In one preferred embodiment, the conduits (2) comprise on their outersurface a series of fins (12) designed to increase their thermalconductivity.

To manufacture the precast segments the reinforcements are disposed on amould that is covered with a countermould for subsequently pouring theconcrete. In one embodiment, the conduits (2) are formed with inserts.Said inserts are disposed joined to the reinforcements of the precastsegment by means of joining elements which are left embedded in it oncethe concrete has set. Either the inserts or the joining elements or bothare rigid, to allow better control of their position with respect to thesurfaces of the mould which will define the flanges of the precastsegment. This guarantees that the distance from the heating cables tothe flanges of the precast segment is always the same.

In the embodiment wherein the conduits (2) are steel pipes (11), theseare disposed interwoven with the reinforcements before pouring of theconcrete to manufacture the precast segments, in such a way that theyform part of said reinforcements. This embodiment is especiallyadvantageous from the point of view of the positioning of the conduitsand resistance they confer on the precast segments. Also, theirmanufacture is simpler, as it is not necessary to carry out anysubsequent unmoulding operation as in the case of the previousalternative.

In specific embodiments wherein the precast segments have one of theirjoint flanges closed, the conduits (2) are blind and the inlet (9)coincides with the outlet (10).

In one embodiment of the invention that works with vertical joints, theconduits (2) are built in a vertical direction, parallel to the verticaljoint flange (3) of the precast segment (6). In another embodiment thatworks with horizontal joints, the conduits (2) are built in a horizontaldirection, parallel to a horizontal joint flange (3) of the precastsegment (6).

In another embodiment, the conduits (2) are built with the samecurvature as the precast segment (6) and with a radial portion (8) atits ends designed to facilitate the introduction of the heating cable(1) into the conduit (2) through the inlet hole (9). In this case, theradial portion (8) of the conduits (2) comprises an elbow joint having acurvature large enough to facilitate the insertion and removal of theheating cable (1).

Likewise, an object of the present invention is a method formanufacturing a wind turbine tower using the precast segments describedabove which allow working even when the ambient temperature is below 5°C. This is a simple manufacturing method which does not make moreexpensive the wind turbine concrete towers that are manufactured withit. Heating cables are used to heat the area of the joint betweenprecast segments and allows said heating cables to be placed quickly andeasily with respect to the joint of the precast segments.

The proposed method for manufacturing wind turbine towers comprises theuse of precast segments such as the ones described above whichincorporate at least one heating cable (1) inside the conduits (2). Themethod comprises a step of disposing the precast segments (6) adjacentto each other, in such a way that a joint (4) is formed between precastsegments. Subsequently, an electrical current is made to flow throughthe heating cables (1), pouring a filler material into the joint betweenprecast segments (6), and finally to remove the heating cables (1) fromthe conduits (2) through the outlet (10) of the conduits (2), once ithas acquired a sufficient degree of setting.

The stage of applying current to heat the precast segments (6) beforepouring the filler material is carried out during sufficient time forthe precast segments (6) to reach a temperature of more than 5° C. Afterpouring the filler material, the current continues to be applied to theheating cables until the filler material of the joint has acquired asufficient degree of setting (understood the level of setting at whichthe filler material has a necessary minimum mechanical resistancecapacity for the joint that encloses it). The time required for thiswill depend on at least the ambient temperature and the type of fillermaterial. In the proposed method the minimum time for which it isnecessary to apply current after pouring the filler material ischaracterised in dependence with the filler material employed. This timemay be several hours, and may even exceed 24 hours when the fillermaterial employed is mortar.

The method described in the present invention may comprise an additionalstage of placing connectors (5) between the ends of different heatingcables (1) that are located in the conduits (2) to allow the flow ofcurrent between said heating cables (1) and carry out the connection toa power supply box for said heating cables (1). When a heating cable (1)is placed in each conduit (2) it is possible to use these connectors (5)to establish the electrical connections between the heating cables (1)in such a way that the current is conducted between the heating cables(1) to reduce the number of connections to the power equipment.

Thanks to the conduits (2) built inside the precast segments (6), theplacing of the heating cables (1) with respect to the joint flanges (3)which form the joints (4) is done quickly and easily. It is onlynecessary to introduce the heating cables (1) through the inside of saidconduits and when they have already been used to heat the mortar pouredinto the joints (4) and these have already set correctly, the heatingcables (1) are extracted from the conduits (2). Therefore, the sameheating cables (1) can be used in the manufacture of several windturbine towers which helps to reduce manufacturing costs.

It must be taken into account that the conduits (2) must be free ofright angles as otherwise, introduction and extraction of the heatingcable (1) is more complex.

In one preferred embodiment, the conduits located close to the flangesthat define the vertical joints are blind and the inlet (9) and outlet(10) coincide such that insertion and removal of the cables is donethrough just one point. Preferably, the conduits are blind and straight,without changes in direction. In this way, the stage of insertion iseven easier. In another embodiment, the inlet and outlet of the conduits(2) close to the flanges that define the vertical joints arethrough-holes. In this way, not only extraction of the heating cables ismade easier, but also their insertion in another precast segment forsubsequent use thereof.

For the described manufacturing method it may be necessary to useconnectors (5) to drive current to each heating cable (1) from powersupply equipment.

Generally, the precast segments (6) used in the method for manufacturingwind turbine towers made of concrete have reinforcements inside. Inthese cases, the method comprises a stage of joining the pipes formanufacturing the conduits to the reinforcements.

When using pipes with a high structural resistance they are preferablyembedded in the precast segment and act as a structural reinforcement ofthe precast segment (6) as well as being the conduits (2) intended toreceive the heating cables (1). In a preferred embodiment, the pipes ofa high structural resistance are made of metal, preferably steel.

Likewise, the pipes may be made of material with a low structuralresistance, such as plastic for example. The difference with respect tothe preceding embodiment is that in this case the conduits (2) do notact as a structural reinforcement, their only function is to allowpassage and guiding of the heating cables (1) through them, however,because they are low cost and are embedded in the concrete theyconstitute an efficient option for the heating system.

In another embodiment of the invention, the inserts used for theconstruction of the conduits (2) are coated with a lubricant materialand the method comprises a stage of removing the conduit (2) from theinterior of the precast segment (6).

These inserts are placed before pouring the mortar and simply removedafter the mortar has set thanks to the lubricant material. Thisembodiment entails a lower requirement of material for the placing ofthe heating cables as the inserts which are used to form the conduits(2) can be reused in several towers and/or precast segments.

When the manufacturing method is used to manufacture wind turbine towerswhich have vertical joints, the conduits (2) are built in a verticaldirection, parallel to a vertical joint flange (3) of the precastsegment (6). This example is illustrated in FIG. 2. In this specificcase, a vertical joint can be appreciated in the end of one precastsegment. Said joint is surrounded by a plurality of conduits (2) wherethe heating cable (1) is introduced.

When the method is used to manufacture wind turbine towers which havehorizontal joints, the conduits (2) are built in a horizontal direction,parallel to a horizontal joint flange (3) of the precast segment (6).This embodiment is represented in FIG. 3.

Additionally, when two precast segments (6) are being joined withhorizontal joints, the conduits (2) are built with the same curvature asthe precast segment (6) and with a radial portion (8) at its endsintended to facilitate the introduction of the heating cable (1) intothe conduit (2). This can also be appreciated in FIG. 3.

The insertion of the heating cable (1) in the conduit (2) is performedusing a lubricant material (7) which facilitates said insertion.

Likewise the method can comprise some final stages of removing theheating cable (1) from the conduit (2) of a precast segment (6) andsubsequently introducing said heating cable (1) into the conduit (2) ofanother precast segment (6).

1. Precast segment for wind turbine tower which comprises at least onejoint flange configured to establish a boundary to the formation of atleast one joint between said precast segment and an adjacent precastsegment using a filler material, wherein it comprises at least oneconduit provided with one inlet and one outlet, located in the vicinityof the at least one joint flange of the precast segment intended tohouse a heating cable.
 2. The precast segment of claim 1 wherein theinside of the at least one conduit houses a heating cable.
 3. Theprecast segment of claim 1 wherein the at least one conduit has acoating intended to facilitate the insertion and removal of some heatingcables in the conduit.
 4. The precast segment of claim 1 wherein thecoating comprises at least one layer of lubricant material.
 5. Theprecast segment of claim 1 wherein it is made of reinforced concrete andthe surfaces which delimit the at least one conduit are made ofconcrete.
 6. The precast segment of claim 1 wherein it is made ofreinforced concrete and the at least one conduit is formed by a pipemade of a material with a high thermal conductivity embedded in theconcrete of the precast segment.
 7. The precast segment of claim 1wherein the precast segments comprise reinforcements inside and theconduits are joined to said reinforcements.
 8. The precast segment ofclaim 1 wherein the precast segments comprise reinforcements in theirinterior and the conduits are made of metal and form part of saidreinforcements.
 9. The precast segment of claim 1 wherein the conduitsare blind and the inlet and the outlet coincide.
 10. The precast segmentof claim 1 wherein the conduits are built in a vertical direction,parallel to a vertical joint flange of the precast segment.
 11. Theprecast segment of claim 1 wherein the conduits are built in ahorizontal direction, parallel to a horizontal joint flange of theprecast segment.
 12. The precast segment of claim 11 wherein theconduits are built with the same curvature as the precast segment andwith a radial portion at its ends designed to facilitate theintroduction of the heating cable in the conduit through the inlet hole,and the radial portion of the conduits comprises an elbow joint having acurvature large enough to facilitate the insertion and removal of theheating cable.
 13. Method for manufacturing a wind turbine tower usingprecast segments for wind turbine towers wherein the precast segmentscomprise: at least one joint flange configured to establish a boundaryto the formation of at least one joint between said precast segment andan adjacent precast segment using a filler material, at least oneconduit provided with one inlet and one outlet, located in the vicinityof the at least one joint flange of the precast segment intended tohouse a heating cable and at least one heating cable located inside theconduits, wherein the method comprises the following stages: disposingthe precast segments adjacent to each other, in such a way that a jointis formed between precast segments, making an electrical current flowthrough the heating cables, pouring a filler material into the jointbetween precast segments, removing the heating cables from the conduitsthrough the outlet of the conduits, once the mortar has acquired asufficient degree of setting.
 14. The method of claim 13 wherein itcomprises a stage of placing connectors between the ends of the heatingcables that are in the conduits allowing the flow electrical currentbetween said heating cables.
 15. The method of claim 13 wherein theconduits used are coated in a lubricant material and the methodcomprises a stage of removing the conduit from the inside of the precastsegment.
 16. The method of claim 13 wherein the insertion of the heatingcable into the conduit is performed using a lubricant material whichfacilitates said insertion.
 17. The method of claim 13 wherein themethod comprises a stage of removing the heating cable from the conduitof one precast segment and a subsequent stage of inserting said heatingcable into the conduit of another precast segment.